Stabilized platens



June 22, 1965 A. N. ORMOND 3,190,108

STABILIZED PLATENS Filed March 20, 1961 INVENTOR. ALFRED N. ORMOND 33 F!G.3. WZQA A TTOPNE Y5 3,190,108 STABILIZED PLATENS Alfred N. Ormond, 11969 E. Slauson, Santa Fe Springs, Calif.

Filed Mar. 20, 1961, Ser. No. 96,797 1 Claim. (Cl. 73-1) r This invention relates to force isolating structures for use in measuring and calibrating force components'developed in relatively large masses. More particularly, it

.has to do with novel structure in the form of stabilized platens for isolating or rendering ineifective various force components and moments to the end that only a desired given force is transmitted either for measuring or calibrating purposes.

While the stabilized platens of this invention have many applications, their preferred use is in conjunction with calibrating load cells in a multi-component test stand such as used for rocket motors, for example, and

for purposes of illustration, the invention will be discussed in this connection.

In the testing of rocket motors, the motor itself may be mounted in a test stand in such a manner that six individual force components corresponding to the six degrees of freedom of a given body may be measured. Thus, the motor supports include three load cells positioned to measure, for example, the thrust, side forces, and vertical forces which are all directed in mutually perpendicular directions. Also, three moment measuring load cells are provided to measure roll, yaw, and pitch. The rocket motor must be suspended in such a manner that the individual components may be measured with a minimum of interaction between the various components. For example, in order to obtain an accurate measurement of thrust, it is important toisolate any forces or moments as a consequence of the presence of the otherfive components.

For greatest accuracy, the load cells for the rocket motor should be calibrated in place. If, however, a calibrator is attached to calibrate the thrust load cell, for example, the stiffness or redundancy with respect to the other five components is altered as a consequence of this physical connection. To overcomethis deficiency, it would be desirable to provide a structure through which no component of force or moment can be transmitted except "the desired component, for example, the component along a given direction corresponding to the thrust axis when thrust calibration is being carried out.

With the foregoing in mind, it is accordingly a primary object of this invention to prOVide an isolating structure or stabilized platen'in which a force may be transmitted only in a given direction and all other force components in directions diiterent from said given direction isolated to the end that the overall stiffness of the particular test stand system with respect to the other load cells is not altered when a calibrating load cell is connected to the system.

Another object is to provide in which only forces in a given directioncan be transmitted and which includes an inherent self-compensating feature such that stillness of the structure is neutralized so that effectively a zero rate spring motion is provided. V i v 7 Another object is to provide a force transmitting member in which the motion thereof is constrained to a precise rectilinear direction so that in certain applications, normal and inverted pendulum effects are eliminated.

Briefly, these and other objects and advantages of this invention are attained by providing a stabilized platen structure in the form of a force transmitting member having first and second flexure supports secured thereto at spaced points in line with the desired given direction a force transmitting means 2 of force transmission. These flexure supports extend in a direction parallel to each other and normal to said given direction. The free ends terminate in a tie plate. The force transmitting member or force plate together with the tie plate and first and second fiexure supports define generally a parallelogram structure such that motion of the force plate is confined to the desired given direction, and any force components or moments in other directions are completely isolated and thus prevented from passing through the force plate.

In one embodiment, the lower tie plate is secured to a stationary structure such as ground or astationary frame constituting part of the test stand. In a second,

embodiment, the structure includes additional flexure supports extending upwardly from the tie plate to termimate in a stationary structure constituting ground or part of the test. stand in a position substantially co-planar with the force plate. The tie plate thus is floating, and the arrangement is such that the given direction of motion of the force plate is precisely rectilinear.

in the use of this structure, the stabilized platens are connected between a calibration load cell and a suitable connecting structure passing to the rocket motor for transmitting force to the rocket motor.

A better understanding of the invention and more particularly of its preferred application will be had by.

ly by way of example, a rocket motor 10 supported in a test stand by suitable load cells 11, 12, and 13, secured to ground G which may constitute a stationary frame structure. As shown, the ends of the respective load cells are connected through flexure pivots such as indicated by the letters a, b; c,'d; and e, 1, respectively. The load cells 11 and 12 maybe employed to measure lateral or up and down forces on the rocket motpr 10 or even to measure pitching movement of the rocket .motor by a combination of the readings of the load cells.

The load cell 13, on the other hand, is designed to measure thrust and towards this end is axially aligned with the longitudinal thrust axis of the motor 10.

Assuming it is desired to calibrate the thrust load cell 13, a known force in the direction of the thrust axis is applied to'the motor 10 and readings of the load cell 13 taken. For this purpose, there is provided a force transmitting-framel l; connected through a force plate 15 supported on first and second flexure supports 16 and 17.

a force supplied by a'jack J, for example, in the direction indicated by the arrow 19. Suitable fiexu're pivots.

for the frame 14, force plate 15, and calibrating load celllfi are provided as shown and are simliar in struc- V ture to the fiexure pivots a through 1.

The other end of 'the' force plate 15 in turn con nects to a calibrating load cell 18 which will measure i Q i 3,190,108

structure, consider first the results of calibrating load cell 18 directly to the structure'14. In

- this event, if a lateral force were exerted on therocket motor such as indicatedbyl the arrow 20 in order to. calibrate-the load cells 11 and 12,.the presence of the}- frame structure 14 in conjunction with the calibrating load cell 18. would change the overall stiffness of the system and the; readings. of the load cells 11 and 12 would thus be diiferent from those obtained when the load j cell 18 was disconnected fromthefram'e14."

If instead, the'force plate .15 of the stabilized platen structure-including the flexure supports .16 and 17 Eisr connected to the frame 14 and the load cell .18 then con- I nected to the force plate 15 as shown in FIGURE 1, a

given reading on the load cells 11 and 12' when calibrating a lateral force will remain the samewhether or not connecting the force plate during its horizontal movementwhen oriented the load cell 18 is connected to the right hand end of the force plate115. This. is because the forceplate 15 isolates all forces except those in the direction ofthe thrust 'axis. The platen may thus remain in the'system and its stillness will become a part ofthe other readings.'

These other readings, however,jwill be consistent whether ,or not the loadcell 18 is connected to the platen.

V and 32rd terminate .at stationary structural points 38' and 39, 4t) 3l1dj41, generally. on the same level or co- Referring now to FIGURE 2, the mannerin-which the desired force component isolation is achieved by the stabilized platen of FIGURE 1 willbe understood. In

FIGURE 2, it will be noted that the force plate 15 is arranged to transmit the pull force Pexerted on the right i 1 handend of the force plate 15 to a corresponding, simulatedthrust force Fat the lefthand end of the'plate'in.

a given direction which inFIGURE 2 is horizontal. The first and second flexure supports Hand 17 e'xtendnormally from this given direction generally in parallel'direc tions to each other. The lower ends are connected together by a tie plate 21 which is' secured ma stationary structuresuch asground G; The. terminal Connections 7 of .the'first and second flexure supports. 16 and 17 are spaced apart 'a distance equal to the distance between the locations of the upper; connections to theforce plate 15 sothat the force plate 15 together withthe tie plate,

Car

21'and flexure supportsdefine, generally a parallelogram. 'As shown in FIGURE 2, each of the flexure supports 7 includes upper and lower flexure webs suchas indicated at. 22 and 23 for the-support 16 and 24 and 25'for. the. support 17. The bending'axes for these flexure webs-are indicated at 22', 23., 24, and 25 and as, is evident from FIGURE 2, these bending axes are generally parallel' to each other and normal to the direction ofthe flexure supports 16 and 17betweenthe'force'plate 15 and tie 1 plate 21. r V v From thefo'regoing structure, it will be evident that movementof the force'plate 15 is constrained to an horizontal direction as viewedxin FIGURE 2 corresponding to the directions of the force designations F. and; P.

All other forces or moments are isolated. For example, any vertical force such as in the direction of the arrow 26 isborneincompression by the flexure supports 16 and 17; Any lateral force, such as indicated by the arrow 27 is also borne by the flexures-16 and 17 as a consequence of their relatively wide width. Similarly, force moment-s such as indicated by the arrows 28, 29., and 30' rather than the force plate 15.

plate '15' moves'to the left or right in a'horizontal direcbeing transmitted. r Inother words, F will remain equal. to forany given position of the force plate 15, .theplate 15 exhibiting essentially a zero springi rate.

In other instances, it may be desirable to avoid any pendulum etiect'since, ..the pendulumvetfect can only opcrate if there is. aslight'vertical displacement of the as shown in FIGURE 2. .iThus, in order to realize a perfect rectilinear movement wherein there .is no..de- 'pression or elevationiof the force plate '15 .when moved horizontally, a .m-odified platen, structure may; .be'employed as illustrated'in'FIGURE .3.

In FIGURE 3, the tie plate 33 iswider than the flexure supports 31 and 32 and can thus accommodate pairs? 7 of fiexures. 34 and-35, and 36 and 37 on either side of v the first andsecond fiexures .31 and 32. These additional,

exures' extend 'in an opposite direction to the flexures 31 planar with the force plate 15'. 1 'The flexure webs ofthe' additional the first-and'second flexure supports 31 and 32 indicated at y. 'Since there are twice as many additional :flexure supports, each of half the widths of the first and second flexure supports the overall stiffness of the flexure sup-. ports 31 andy32 is equal to'the overall stiffness ofxthev flexure supports :34,'35,36,.and.37; a a

'With the foregoing'structure' and'the stabilizedplate secured to a stationary structure through the supports 38, 39, 40, and 41, a folded fiexure'support structure is.

provided wherein horizontal'rnovement of the-force plate 15' will be 'constrained'to an exact rectilinear; path, there being no elevation 'or lowering of the plate 15. i

when movement takes place; This result is achievedby permittingthe lower tie plate 33 to'.float;that; is, any

elevation or lowering movement as a consequence ofbending of the flexures will be reflected in the tie plate tion; the tie plate 33 will be brought slightly closer to the force. plate 15 in the manner of a collapsing parallelogram with the top side of the parallelogram held at a given are respectively absorbed within the flexu're supports so that. the only force which can be"transrnitted'is in the given direction corresponding to the direction of :the'

arrows F and P. e r 7 I a V It willgbe evident that YaHY IIIOVE IIIGHtsOf the force 2,2.through 25.. Itis possibleto weight the force plate:

in such a rnanner that the inverted pendulum effect will result in-the generation of forces which will exactly plate from left to right, or from right ,to left, willbe o'p-v 1 posed ;by the spring stiffness o f. the .various flexure webs i cancel the stiffness forces exerted by the flexure 'webs.

- By so weightingthe force plate 15, the movement of the force plate'in thegiven directionvof force,transrnis- 'sion will notadd or subtract from the particular force as limited to this one function.

levelso that the under side swings up towards or away from the top side during movement. z

The folded stabilized platen. structure of FIGURE 3 o is used when it "is necessary that the force transmitting plate 15move'in an exactly rectilinear path in order to avoid the introduction of any spurious. forces;

. From the foregoing description, it will be evident that the present inventionhas provided. novel means for 'increasing the accuracy. of testing and calibrating rocket motorsin a'test stand. .While only. the one'specific applicationof the ,invention has" been set forth and. de- 7 .thought of -in said force is isolated from any force components in. directions other than said given direction, comprising, in combination:- a flat force and motion transmitting plate extending between said .end points with the ends of said platecoinciding with said .end pointsga tieplate inspaced parallel ,relationship to said forceplate;.first and second support means secured at upper ends to said force plate at locations spaced along said given direction andflat lower ends to said tie plate at locations spacedalongf In FIGURE 3, the forcegplate is designated 15's. and is again supported by first and. second fiexuresxSI and 32, the lower terminal ends of which are connected together by a tie plate'33.-i

flexure supports 34' through 37 are co-planar with the flexure webs in the basic first and second flexure supports 3l and 32. Furthen. the width of each; of the additional flexure webs indi-i cated atx are each made equal to one-half the widthof Thus, when. the force.

a line parallel to said given direction corresponding to the spacing between said first mentioned locations to de fine a parallelogram type structure, each of said support means including upper and lower flexure webs coplanar with each other and lying in a plane normal to said given direction, said flexure webs being respectively positioned adjacent to the points of securem'ent of said support means to said force plate and tie plate respectively for flexing movement about parallel axes lying in said plane and parallel to said force plate; and two pairs of additional support means, the support means of one pair being positioned on either side of said first support means with their lower ends secured to said tie plate and their upper ends secured to a stationary structure co-planar with said force plate; and the support means of the other pair being positioned on either side of said second support means with their lower ends secured to said tie plate and their upper ends secured to a stationary structure coplanar with said force plate, each of said additional support means including flexure Webs adjacent their upper and lower ends co-plan-ar and at corresponding levels with the ilexure webs of said first mentioned first and second support means respectively, and being of one half the Width of the fixure webs in said first mentioned support means whereby the total stifiness of said first and second support means equals the total stillness of said additional support means and whereby said [force plate is constrained for movement only in said given direction.

References Cited by the Examiner UNITED STATES PATENTS 2,085,687 6/37 Peters 33--147 2,976,734 3/61 Gindes et al. 73-517 X 2,997,875 8/61 Moore 73-l41 ISAAC LISANN, Primary Examiner. 

